The present invention relates to a communication device for transmitting and receiving control and user data bursts in a digital telecommunication system and to a method for distinguishing between data bursts of a first type transmitted from a first communication device and data bursts of a second type different from said first type transmitted from a second communication device in a digital telecommunication system. The communication device of the present invention can be a base station or a mobile terminal of the telecommunication system. The first communication device and the second communication device can be a base station and a mobile terminal, respectively, or two mobile terminals directly communicating with each other. The present invention particularly enables the distinction of the traffic direction of received data bursts.
In a digital radio telecommunication system, one base station usually serves and communicates with several mobile terminals or user equipment terminals in predetermined cells. The transmission of data from the base station to the mobile terminals is called downlink and the transmission of data from the mobile terminals to the base station is called uplink. In some telecommunication systems, a direct communication of data bursts between the mobile terminals is possible. The data, which can be either control data or user data, e. g. speech data, are transmitted in data bursts. For the transmission of data bursts, several transmission channels are defined. The transmission channels depend on the particular telecommunication system in use. In each telecommunication system, however, transmission channels for the transmission of synchronization data, control data and user data are necessary. By means of the synchronization data, the mobile terminals synchronize their time frames to the timing of the base stations. The control data channels are e. g. used by the base stations to transmit broadcast control data to all mobile terminals in the respective cell. The synchronization channel can be part of a control channel, for example the broadcast control channel. The data channels are used by the mobile terminals to transmit user data to the base stations and by the base stations to transmit user data to the mobile terminals.
An example of the time frame structure of a media access control channel (MAC) comprising the most common channels is shown in FIG. 1. The MAC frame structure shown in FIG. 1 comprises a control channel, e. g. a broadcast control channel (BCCH) used by the base stations to broadcast control data to all mobile terminals in the respective cells, traffic channels for uplink or downlink transmission of user data and a random access channel (RACH). The random access channel is used by the mobile terminals to transmit service requests to the base stations. E. g. if a mobile terminal needs a user data channel for transmitting user data to a base station, the mobile terminal sends a service request via the random access channel to the base station. The base station receiving the service request answers the request by sending a corresponding grant or refusal message back to the mobile terminal.
As shown in FIG. 1, the different channels comprise training sequences, preambles and/or headers. Training sequences or synchronization headers are mainly used for an accurate synchronization of the receiving unit, i. e. a base station or a mobile terminal receiving data bursts on a transmission channel to enable a reliable reception and use of the transmitted data. E. g., a training sequence consists of a predetermined number of repetition patterns or symbols, whereby each symbol consists of a certain number of samples. Typically, all symbols or repetition patterns in a given training sequence are identical, i.e. have the same shape or content.
Looking at the example of the GSM-system (global system for mobile communications), the normal user data bursts, the synchronization bursts and the random access bursts each comprise a training sequence. In the normal user data burst, the training sequence is located in the middle of a time slot and comprises 26 bits. In a synchronization burst the training sequence is also located in the middle of a time slot, but comprises 64 data bits. In a random access burst, the training sequence is located in the front part of the time slot and comprises 41 bits. In this case, a communication device receiving different types of data bursts can easily distinguish the different types of data bursts by their different training sequences and downlink and uplink data bursts can be recognized without problems. A mobile terminal therefore can distinguish easily between a broadcast control data burst broadcast from a base station to all mobile terminals in the corresponding cell and user data bursts or random access bursts transmitted from other mobile terminals to the base station. However, the use of training sequences of different length or shapes for the different types of data bursts requires a complex detector structure in the receiving unit, because the receiving unit has to deal with many different types of training sequences.
Depending on the multiple access scheme used in the telecommunication system, e. g. frequency division multiple access, time division multiple access or code division multiple access, a mobile terminal may have other criteria, e. g. frequency or code, available to distinguish if the data bursts have been transmit from a base station or from other mobile terminals. In this case, even the use of identical training sequences in the different types of data bursts may be possible. However, if no other criteria are available, as e. g. in a time division duplex mode (TDD mode), in which the same carrier frequency is used, a mobile terminal cannot distinguish if the data bursts are coming from a base station of from other mobile terminals when identical training sequences are used in the different data bursts.
The object of the present invention is therefore to provide a communication device for transmitting and receiving control and user data bursts in a digital telecommunication system, which is able to distinguish between different types of data bursts in an easy and simple way. The object of the present invention is further to provide a method for distinguishing between data bursts of first type transmitted from a first communication device and data bursts of a second type different from said first type transmitted from a second communication device in a digital telecommunication system.
The above object is achieved by a communication device for transmitting and receiving control and user data bursts in a digital telecommunication system according to claim 1, which comprises receiving means for receiving data bursts including data bursts of a first type and data bursts of a second type different from said first type, said first type bursts respectively comprising a first training sequence and said second type bursts respectively comprising a second training sequence. The communication device further comprises correlation means for auto-correlating the data of received data bursts and outputting an auto-correlation result and recognizing means for recognizing the type of a received data burst on the basis of a phase value of the auto-correlation result of the training sequence of said burst. A communication device of the present invention can be a mobile terminal or a base station of the telecommunication system.
The above object is further achieved by a method for distinguishing between data bursts of a first type transmitted from a first communication device and data bursts of a second type different from said first type transmitted from a second communication device in a digital telecommunication system, said first type data bursts respectively comprising a first training sequence and said second type data bursts respectively comprising a second training sequence, which comprises the steps of receiving a data burst, auto-correlating the data of said received data burst and outputting an auto-correlation result and recognizing the type of the received data burst on the basis of a phase value of the auto-correlation result of the training sequence of said data burst. The first communication device can be a base station and the second communication device can be a mobile terminal of the telecommunication system. Alternatively, the first communication device as well as the second communication device can be mobile terminals of the telecommunication system.
The communication device and the distinguishing method of the present invention particularly enable the distinction between different traffic directions. Thereby, a receiving communication device is able to distinguish if a received data burst is of interest or not.
The present invention thus enables the use of training sequences with very similar shapes in the different types of data bursts used for different traffic directions, e. g. for the uplink and the downlink in the telecommunication system, so that the general structure of the communication devices in the telecommunication system is significantly simplified. Particularly, very similar structures for generating the training sequences on the transmitter side and for correlating the received training sequences on the receiver side in the different communication devices can be provided. Further, a single detecting or recognizing structure can be used in the communication device for all different types of data bursts. Thus, the communication devices can be built in a simple and cost-effective way.
The training sequences of different types of bursts can be formed with a very similar content or shape, but have to result in different phase values at the output of the auto-correlation means on the receiving side so that the different types of data bursts can be distinguished. Thus, the communication device of the present invention is able to distinguish between different types of data bursts in a simple and easy way.
The training sequences used in the different types of data bursts can but do not need to have an identical length as long as they result in a different phase information in the auto-correlation result on the receiver side. Thus, the content and the length of the different training sequences used in the different types of data bursts can be different from each other. If, e. g. the first training sequence has a length of 8 symbols and the second training sequence has a length of 6 symbols, whereby each symbol has the same number of samples, the amplitude of the auto-correlation peak might be different. However, the important characteristic for the present invention is that the phase information of the auto-correlation result for the two training sequences is different so that the different types of data bursts can be distinguished. Even when the training sequences have different length, the same auto-correlator structure on the receiver side can be used.
The present invention presents the concept of a digital telecommunication system, in which the base stations transmit data bursts of a first type including a first training sequence and the mobile terminals transmit data bursts of a second type including a second training sequence or vice versa. In other words, the base stations advantageously transmit the same first (or second) training sequence in all the different data bursts having a training sequence and the mobile terminals similarly transmit the same second (or first) training sequence in all their data bursts having a training sequence. Alternatively or additionally, different mobile terminals of the telecommunication system can transmit data bursts having respective different training sequences. E. g. a first mobile terminal may transmit data bursts of a first type including a first training sequence and a second mobile terminal may transmit data bursts of a second type including a second training sequence. Thus, a receiving device, as e. g. a base station or a mobile terminal, is able to distinguish the traffic direction of received data bursts. Thereby, the first training sequences and the second training sequences are different from each other, but have a very similar shape. The shape of the first and the second training sequences, respectively, are chosen so that the result of an auto-correlation procedure on the receiver side shows different phase values for the first and the second training sequence, respectively, so that they can be clearly distinguished. Thus unnecessary processing and energy waste in the receiving communication device can be avoided on the basis of the distinction if the received data burst is of interest or not.
Advantageously, the recognizing means of the communication device according to the present invention comprises means for detecting the phase of the auto-correlation result of the training sequence. In this case, the recognizing means can further comprise means for comparing the detected phase with a predetermined phase threshold to recognize the type of the received data burst. This first alternative enables a very accurate phase determination, which can be further used for the calculation of an accurate value of the frequency offset of the transmitted data bursts.
In a second alternative, the recognizing means advantageously comprises means for detecting the sign value of the real part of the auto-correlation result of the training sequence and means for determining the type of the received data burst on the basis of said sign value. This second alternative enables a very simple structure of the recognizing means, since only the sign value has to be looked at.
Further advantageously, in said first training sequence every symbol or pattern is inverted in relation to the respective preceding symbol or pattern but not in said second training sequence, so that the different phase characteristics of the respective auto-correlation results enable a simple recognition of the type of the received data burst. Typically, the samples of the symbols of the training sequences are complex values, so that inverting one symbol in relation to another symbol means that the samples of the one symbol are the negative complex values of the samples of the other symbol. The content, i. e. the absolute values, of the samples and thus the symbols of the different data bursts can be the same or different for the different data burst types.
Further advantageously, all symbols of said first and second training sequence respectively consist of the same number of samples and have an identical absolute value. This greatly simplifies the general design of the communication devices, since all devices can be built with almost the same generating and receiving means for the training sequences. Although the first and second training sequences differ very little from each other, the auto-correlation result gives different phase values for the first and the second training sequence, respectively, so that a clear distinction between the different data burst types is possible.
Advantageously, the communication device according to the present invention is a mobile terminal of the telecommunication system. Thereby, the first type burst is a downlink data burst from a base station and the second type burst is an uplink data burst from another mobile terminal.